/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.client;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.client.ClientHttpResponse;
import org.springframework.http.converter.GenericHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.util.Assert;

import java.io.IOException;
import java.lang.reflect.Type;
import java.util.List;

/**
 * Response extractor that uses the given {@linkplain HttpMessageConverter entity
 * converters} to convert the response into a type {@code T}.
 *
 * @author Arjen Poutsma
 * @see RestTemplate
 * @since 3.0
 */
public class HttpMessageConverterExtractor<T> implements ResponseExtractor<T> {

    private final Type responseType;

    private final Class<T> responseClass;

    private final List<HttpMessageConverter<?>> messageConverters;

    private final Log logger;

    /**
     * Creates a new instance of the {@code HttpMessageConverterExtractor} with the given
     * response type and message converters. The given converters must support the response
     * type.
     */
    public HttpMessageConverterExtractor(Class<T> responseType, List<HttpMessageConverter<?>> messageConverters) {
        this((Type) responseType, messageConverters);
    }

    /**
     * Creates a new instance of the {@code HttpMessageConverterExtractor} with the given
     * response type and message converters. The given converters must support the response
     * type.
     */
    public HttpMessageConverterExtractor(Type responseType, List<HttpMessageConverter<?>> messageConverters) {
        this(responseType, messageConverters, LogFactory.getLog(HttpMessageConverterExtractor.class));
    }

    @SuppressWarnings("unchecked")
    HttpMessageConverterExtractor(Type responseType, List<HttpMessageConverter<?>> messageConverters, Log logger) {
        Assert.notNull(responseType, "'responseType' must not be null");
        Assert.notEmpty(messageConverters, "'messageConverters' must not be empty");
        this.responseType = responseType;
        this.responseClass = (responseType instanceof Class) ? (Class<T>) responseType : null;
        this.messageConverters = messageConverters;
        this.logger = logger;
    }

    @SuppressWarnings("unchecked")
    public T extractData(ClientHttpResponse response) throws IOException {
        if (!hasMessageBody(response)) {
            return null;
        }
        MediaType contentType = getContentType(response);

        for (HttpMessageConverter messageConverter : this.messageConverters) {
            if (messageConverter instanceof GenericHttpMessageConverter) {
                GenericHttpMessageConverter genericMessageConverter = (GenericHttpMessageConverter) messageConverter;
                if (genericMessageConverter.canRead(this.responseType, null, contentType)) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Reading [" + this.responseType + "] as \"" +
                                contentType + "\" using [" + messageConverter + "]");
                    }
                    return (T) genericMessageConverter.read(this.responseType, null, response);
                }
            }
            if (this.responseClass != null) {
                if (messageConverter.canRead(this.responseClass, contentType)) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Reading [" + this.responseClass.getName() + "] as \"" +
                                contentType + "\" using [" + messageConverter + "]");
                    }
                    return (T) messageConverter.read(this.responseClass, response);
                }
            }
        }
        throw new RestClientException(
                "Could not extract response: no suitable HttpMessageConverter found for response type [" +
                        this.responseType + "] and content type [" + contentType + "]");
    }

    private MediaType getContentType(ClientHttpResponse response) {
        MediaType contentType = response.getHeaders().getContentType();
        if (contentType == null) {
            if (logger.isTraceEnabled()) {
                logger.trace("No Content-Type header found, defaulting to application/octet-stream");
            }
            contentType = MediaType.APPLICATION_OCTET_STREAM;
        }
        return contentType;
    }

    /**
     * Indicates whether the given response has a message body. <p>Default implementation
     * returns {@code false} for a response status of {@code 204} or {@code 304}, or a {@code
     * Content-Length} of {@code 0}.
     *
     * @param response the response to check for a message body
     * @return {@code true} if the response has a body, {@code false} otherwise
     * @throws IOException in case of I/O errors
     */
    protected boolean hasMessageBody(ClientHttpResponse response) throws IOException {
        HttpStatus responseStatus = response.getStatusCode();
        if (responseStatus == HttpStatus.NO_CONTENT ||
                responseStatus == HttpStatus.NOT_MODIFIED) {
            return false;
        }
        long contentLength = response.getHeaders().getContentLength();
        return contentLength != 0;
    }

}
